1. Field of the Invention
The present invention relates to a liquid crystal display device, a polarization element used therefor, and a method for manufacturing the polarization element.
2. Description of the Related Art
Display devices are a medium for transmitting information visually to people and play an important role for people and groups in the sophisticated modern information society. The performance of liquid crystal display devices has significantly increased in recent years, and liquid crystal display devices have been adopted as display devices for cellular phones, personal computers, large screen televisions, and the like. Liquid crystal display devices are generally formed of a liquid crystal display panel and a backlight (illumination device) that is placed on the rear side of the liquid crystal display panel and illuminates the liquid crystal display panel with light. In the case where a color image is displayed, each pixel is formed of three sub pixels that correspond to the three primary colors of red, blue, and green, for example, and the sub pixels that correspond to the respective colors are controlled independently so that various colors are reproduced.
At present, the range of application of the liquid crystal display device to mobile devices such as cellular phones and digital cameras is expanding, and there is an increasing demand for the liquid crystal display device that is further reduced in thickness while achieving a higher contrast. Currently, small and medium-sized mass-produced liquid crystal display panels have been reduced in thickness to around 1 mm, and the smallest thickness of such a liquid crystal display panel officially recognized is 0.56 mm. In order to reduce the thickness of a liquid crystal display panel, it is necessary to reduce the thickness of members, such as a polarizer, forming the liquid crystal display panel. In a case where the thickness of a liquid crystal display panel is 0.56 mm, the polarizer has a thickness of 0.1 to 0.2 mm.
Polarizers which are currently available include a film-type polarizer and a thin film polarizer. The thin film polarizer may be reduced in thickness to 1/1000th of the film-type polarizer. A conventional film-type polarizer is formed of, for example, a poly-vinyl alcohol (PVA) resin, iodine, and a protection layer, in which the PVA resin mixed with iodine is drawn so that the dye molecules are unidirectionally aligned. In contrast, the thin film polarizer is formed of a dye (and a protection layer as necessary), and hence the thin film polarizer may be made smaller in thickness than the film-type polarizer. The dye in the thin film polarizer is aligned by a shear stress applied when the dye molecules are coated or by an alignment force of a base material. Technologies used for the above-mentioned thin film polarizer have been reported in Y. Ukai et al., “Current Status and Future Prospect of In-Cell Polarizer Technology”, SID 04 DIGEST, pp. 1170-1173, 2004, Ir Gvon Khan et al., “Ultra-Thin O-Polarizers' Superiority over E-Polarizers for LCDs”, SID 04 DIGEST, pp. 1316-1319, 2004, JP 2006-146116 A, JP 2006-91393 A, and JP 2008-89966 A.